Internal combustion engines typically use either a mechanical, electrical or hydro-mechanical valve actuation system to actuate the engine valves. These systems may include a combination of camshafts, rocker arms and push rods that are driven by the engine's crankshaft rotation. When a camshaft is used to actuate the engine valves, the timing of the valve actuation may be fixed by the size and location of the lobes on the camshaft.
Hydraulic lost motion valve actuation systems may be driven with a cam, particularly those used for an internal combustion engine. The hydraulic displacement of an engine valve in such a lost motion system is directly proportional to the displacement provided by the cam during normal operation. In some applications, however, the engine valve must be closed at an earlier time than that provided by the cam profile. This earlier closing may be carried out by rapidly releasing hydraulic fluid to an accumulator in the lost motion system or to the oil sump. In such instances engine valve seating control may be required because the rate of closing the valve is governed by the hydraulic flow to the accumulator or sump instead of by the fixed cam profile. Engine valve seating control may also be required for applications (e.g. centered lift) in which the engine valve seating occurs on a high velocity region of the cam. Still further, engine valve seating control may be required in common rail Variable Valve Actuation (VVA) designs, in which all seating events occur as a result of the release of hydraulic fluid, possibly to an accumulator.
An example of known systems and methods for controlling valve seating velocity are disclosed in U.S. Pat. No. 6,302,370 to Schwoerer et al., which is hereby incorporated by reference.
It is an advantage of some, but not necessarily all, embodiments of the present invention to provide methods and systems for seating an engine valve using hydraulically actuated components.